Titanium-based carbonitride alloys, so called cements, are produced by powder metallurgical methods and comprise carbonitride hard constituents embedded in a metallic binder phase. The hard constituent grains generally have a complex structure with a core surrounded by a rim of a different composition. In addition to titanium, group VIa elements, normally both molybdenum and tungsten, are added to facilitate wetting between binder and hard constituents and to strengthen the binder by means of solution hardening. Group IVa and/or Va elements, e.g. Zr, Hf, V, Nb, and Ta, are also added in all commercial alloys available today. The carbonitride forming elements are usually added as carbides, nitrides and/or carbonitrides. Historically, the binder phase in cermets has been nickel, most likely because Ti has a high solubility in Ni to facilitate sufficient wetting to obtain a low porosity level. During the 1970s a solid solution binder of cobalt and nickel was introduced. This was probably made possible by improved raw material quality, in particular, a lower impurity level of oxygen. Today all commercial alloys contain 3-25 wt % of a solid solution binder with relative proportions Co/(Co+Ni) in the range 50-75 at %.
Cermets are today well established as insert material in the metal cutting industry. Compared to WC--Co based materials, cermets have excellent chemical stability when in contact with hot steel, even if the cermet is uncoated, but have substantially lower strength. This makes them most suited for finishing operations, which generally are characterized by limited mechanical loads on the cutting edge and a high surface finish requirement on the finished component. Unfortunately, cermets suffer from unpredictable wear behavior. In a worst case, complete tool failure is caused by bulk fracture which may lead to severe damage of the work piece as well as tool holder and machine. More often, tool failure is caused by small edge line fractures, which abruptly change the surface finish or dimensions obtained. Common for both types of damages is that they are stochastic or sudden in nature and occur without previous warning. For these reasons cermets have a relatively low market share especially in modern, highly automated production which relies on a high degree of predictability to avoid costly production stops.
One way to improve predictability would be to increase the toughness of the material and work with a larger safety margin. However, so far this has not been possible without simultaneously reducing the wear and deformation resistance of the material to a degree, which substantially lowers productivity.